A planet with a thin atmosphere is considered to have a low atmospheric pressure. This means the air is less dense and exerts less pressure on the surface.

Here are some characteristics of a planet with a thin atmosphere:

* Less air to breathe: The lack of a substantial atmosphere means less oxygen for humans and other life forms that require it.

* Extreme temperature fluctuations: Without a thick atmosphere to trap heat, the surface temperature can fluctuate greatly between day and night.

* Weak protection from radiation: The thin atmosphere offers little protection from harmful solar radiation.

* Less weather phenomena: The lack of a thick atmosphere can lead to fewer clouds, storms, and wind.

Examples of planets with thin atmospheres include:

* Mercury: It has a very thin atmosphere composed mainly of sodium, potassium, and helium.

* Mars: While having a thin atmosphere, it is thicker than Mercury's and consists mainly of carbon dioxide.

It's important to note that a "thin atmosphere" is relative. Even planets with very thin atmospheres can have some important effects on the planet's surface and climate.